. . "Still more preferably Ar is a group where X is O, S, SO, SO2, SNR4, S(O)NR4, NR4 or NC(O)CH2OR4, where R4 is selected from hydrogen, R5 and ???C(O)R5 groups where R5 is C1-8hydrocarbyl optionally substituted with one or more hydroxy, fluorine or chlorine groups; R6 and R7 are independently selected from hydrogen, methyl and cyano groups; and R8 and R9 are independently selected from hydrogen, fluo" . .